Amalgamated Society of Engineers v Adelaide Steamship Co Ltd (“Engineers' Case”) (1920) 28 CLR 129

This case considered s.51(xxxv) involving the power  of the Commonwealth for conciliation and arbitration in relation to industrial disputes when they extended beyond the limits of one State.  The central issue was whether or not the Commonwealth could use this power to make laws which were binding on the States as employers.  It is arguably the most important case in constitutional law.